Conventionally, a step motor driven valve having a cam mechanism (hereinafter referred to as a cam valve), has the structure disclosed, for example, in Japanese Published Unexamined Utility Model Application No. S61-117971 (Reference Document 1) and Japanese Published Unexamined Utility Model Application No. S61-117972 (Reference Document 2).
The cam valve is configured to include: a valve box having a fluid passage and valve seat; a valve body that rests on and moves away from the valve seat of the valve box; an elastic body that biases the valve body in a direction away from the valve seat; a valve rod that is coupled to the valve body and is supported to freely ascend and descend to the top lid of the valve box; a cam plate that contacts the cam roller at an upper end of the valve rod to push down the valve rod; and a pulse motor (step motor) that rotates and drives the cam plate. When the cam plate is rotated by the pulse motor to push down on the valve rod, the valve body at the lower end part of the valve rod rests on the valve seat.
This step motor driven cam valve is capable of performing highly accurate flow rate control and exhibits an excellent practical effect.
In the cam valve using the step motor, the cam plate is rotated by a predetermined angle according to the number of pulses supplied to the step motor, and the valve rod and the valve body are minutely deformed by the rotation of the cam plate so as to perform fluid flow rate control. Thus, this valve needs to be zero-point adjusted so that the valve body, the valve rod, etc., are positioned exactly to a zero-point position (a fully opened position or a fully closed position) when fully opening or fully closing the valve.
That is, the valve needs to be adjusted so that when fully opening the valve, a minimum radius portion of the cam plate contacts the cam roller and the valve body and the valve seat are kept furthest apart. On the other hand, when fully closing the valve, the valve needs to be adjusted so that a maximum radius portion of the cam plate contacts the cam roller and the valve body rests on the valve seat with an appropriate force.
Since the aforementioned conventional step motor driven cam valve has no adjusting mechanism for positioning and adjusting the valve body to the zero-point position, it takes a considerable amount of time and effort to zero-point adjust the valve, which is a problem.
Further, unless the processing accuracy and assembly accuracy of each constituent component of the cam valve are increased, the valve body is excessively pressed to the valve seat, or the contact between the valve body and the valve seat is insufficient, resulting in damage to the valve seat and leaking fluid.    [Patent Document 1] Japanese Published Unexamined Utility Model Application No. S61-117971    [Patent Document 2] Japanese Published Unexamined Utility Model Application No. S61-117972